New research published in the journal PLoS ONE this month finds that the US Endangered Species Act (ESA) is effectively aiding in the recovery of beleaguered populations of marine mammals and sea turtles.

Marine mammals and sea turtles comprise 62 of the 163 marine species that are currently afforded ESA protections. Researchers collected annual abundance estimates for populations of all 62 of those marine mammal and sea turtle species in order to analyze population trends and the magnitude of observed changes in population numbers.

The research team hypothesized that populations that have been listed under the ESA for longer periods of time would be more likely to be recovering than those species listed recently, regardless of whether they were listed as “threatened” or the more severe “endangered,” and that’s exactly what they found.

New research published in the journal PLoS ONE this month finds that the US Endangered Species Act (ESA) is effectively aiding in the recovery of beleaguered populations of marine mammals and sea turtles.

Extinction risks for many of the species that call Earth’s oceans home have increased as the impacts of human activities, such as overfishing, habitat loss, pollution, and climate change, have caused the degradation of marine ecosystems. This, in turn, has led to a growing number of marine species being listed under the ESA.

Mammals like humpback whales and sea turtles comprise 62 of the 163 marine species that are currently afforded ESA protections. Abel Valdivia of the Center for Biological Diversity in California led a research team that collected annual abundance estimates for populations of all 62 of those marine mammal and sea turtle species in order to analyze population trends and the magnitude of observed changes in population numbers.

Of those 62 species (which includes species in addition to some subspecies and distinct population segments), the researchers chose to focus on the recovery status of 23 representative populations of 14 marine mammal species and eight representative populations of five sea turtle species that not only occur but also reproduce in U.S. waters. All of the populations that were the focus of the study were listed under the ESA before 2012.

More than three-fourths of the marine mammal and sea turtle populations that Valdivia and team studied have seen substantial population increases. The researchers report that 18 of the marine mammal populations and six of the sea turtle populations “significantly increased after ESA listing,” while two marine mammal populations and no sea turtle populations were found to have declined after being granted ESA protections. Three marine mammal populations and two sea turtle populations showed “non-significant changes.”

Valdivia and colleagues hypothesized that populations that have been listed under the ESA for longer periods of time would be more likely to be recovering than those species listed recently, regardless of whether they were listed as “threatened” or the more severe “endangered,” and that’s exactly what they found.

“Overall, the 24 populations that increased in abundance were from species listed for 20 years or more (e.g., large whales, manatees, and sea turtles),” the researchers write in the study. “Conservation measures triggered by ESA listing such as ending exploitation, tailored species management and fishery regulations, and other national and international measures, appear to have been largely successful in promoting species recovery, leading to the delisting of some species and to increases in most populations.”

The study includes case studies of how the ESA has been an important tool for helping the Hawaii population of humpback whales, the western population of Steller sea lions, and the North Atlantic population of green sea turtles rebound. For instance, the authors note that the ESA prohibited the harvesting of adult turtles and their eggs, which helped ensure that mature and reproductive adults are not removed from the North Atlantic population of green sea turtles, who mostly nest on Florida’s beaches. At the same time, fishery regulations instituted as a result of ESA listing helped reduce green sea turtle bycatch from pelagic longlines and gillnets in the Atlantic, the pound net fishery in Chesapeake Bay, and the shrimp and flounder trawl fisheries in the Gulf of Mexico.

“ESA protections and several local and international conservation efforts have been important for the recovery of green sea turtles in the North Atlantic and other regions,” the researchers write. “ESA regulations have led to fishing gear modifications, major changes in fishing practices, time and area closures, and the establishment of turtle excluder devices for shrimp trawlers.” The result is a conservation success story for green sea turtles: “The species has been increasing exponentially.”

The researchers say their findings support the conclusions of previous studies that looked at a variety of terrestrial taxa, marine birds, and fish and determined that the longer they are listed under the ESA, the better their chances of bouncing back. Just as importantly, they write in the study, “Our results also support previous studies that highlight the capacity of marine mammals and sea turtles to rebound from decades of exploitation after coordinated national and international conservation efforts.”